addEventListener('click', function () {
//创建Promise
const p = new Promise((resolve, reject) => {
    //1.创建对象
    const xhr = new XMLHttpRequest();
    //2. 初始化
    xhr.open('GET', 'https://api.apiopen.top/getJoke');
    //3.发送
    xhr.send();
    //4. 处理响应结果
    xhr.onreadystatechange = function () {
        if (xhr.readystate === 4) {
            //判断响应状态码2xx
            if (xhr.status >= 200 && xhr.status < 300) {
                //控制台输出响应体
                resolve(xhr.response);
            } else {
                //控制台输出响应状态码
                reject(xhr.status);
            }
        }
    }
});
p.then(value => {
    console.log(value);
},
    reason => {
        console.log(reason);
    })
});
